Use containerd client.

[Random-Liu]

Containerd is adding a new client, which will make integration and our unit test much easier.

We should use it after it lands.

containerd/containerd#904

[mikebrow]

Looks nice.. will have to see if it does all we need.

[Random-Liu]

Just a note here, the so-called AgentFactory could be removed after we switch to new containerd client.

Only the log redirection and decoration logic need to be kept.

[Random-Liu]

Given that:

1. The timeframe is pretty tight;
2. Containerd client may miss some features we need, e.g. some image functions.

I propose the following plan:

• [P0] Upgrade to new containerd API, and make it work. (PR: Switch to new containerd api #78)
• [P1] Replace all service clients with "client.service" (containerd expose all services directly). (PR: Use containerd client library to connect to containerd services #82)
• [P0] Cut the alpha.1 release, which I think highly possibly will be our final alpha release version.
• [P2] Switching each function to use actual new containerd client functions one by one.

@kubernetes-incubator/maintainers-cri-containerd
/cc @crosbymichael @stevvooe

[Random-Liu]

Change this to v0.2.0. I don't think we have time to switch to the new client. Making sure we are using new containerd api is good enough for this release.

@mikebrow Let's finish the second step in this release and leave the client switch to next one.